An electric vehicle (including a fuel-cell vehicle and a hybrid vehicle) includes a high voltage power source (a main power source) for a traction motor and a low voltage power source (an auxiliary power source) for an auxiliary device. The “auxiliary device” is a generic term for vehicle-mounted devices that have an operating voltage lower than a voltage of the traction motor. The operating voltage of the vehicle-mounted devices is equal to or lower than approximately 50 volts. The traction motor has a driving voltage higher than 100 volts, and the main power source has an output voltage exceeding 100 volts. In other words, the auxiliary power source has an output voltage lower than the output voltage of the main power source. Typical examples of the main power source are a lithium-ion battery and a fuel cell. A secondary battery, which is rechargeable, is adopted as the auxiliary power source. A typical example of the auxiliary power source is a lead battery. Japanese Patent Application Publication No. 2017-085810 and Japanese Patent Application Publication No. 2016-135010 illustrate such power source systems.
The main power source is connected to a power converter via a system main relay. The power converter converts power from the main power source into driving power of the traction motor. The power converter includes a capacitor connected between a positive electrode and a negative electrode of the main power source. The capacitor is provided for smoothing a current supplied from the main power source or for temporarily storing power energy in a chopper-type voltage converter. When the system main relay is closed and the power converter is connected to the high voltage power source at turn-on of a main switch of the vehicle, a large current flows into the capacitor through the system main relay. The surge of the large current may cause contact melting in the system main relay. In this respect, in the power source system in each of Japanese Patent Application Publication No. 2017-085810 and Japanese Patent Application Publication No. 2016-135010, the capacitor is charged by using an auxiliary battery prior to switching the system main relay to a connected state. Charging the capacitor before switching the system main relay to the connected state is referred to as pre-charging.
The power source system in each of Japanese Patent Application Publication No. 2017-085810 and Japanese Patent Application Publication No. 2016-135010 includes a boost converter having a low voltage terminal thereof connected to the auxiliary power source and a high voltage terminal thereof connected to the power converter without interposing the system main relay. A controller of the power source system pre-charges the capacitor with power from the auxiliary power source by operating the boost converter prior to switching the system main relay to the connected state.
To ensure execution of the pre-charging even in a case where a remaining amount in the auxiliary power source is small, the power source system in Japanese Patent Application Publication No. 2016-135010 activates only an auxiliary device required for the pre-charging, while prohibiting activation of another auxiliary device.